Young marsupial (3)
I believe the answer is:
roo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">young marsupial</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for roo that I've seen before include "short jumper" , "young skipper" , "Aussie jumper!" , "Marsupial (dim.)" , "Marsupial (informal)" .)